JPH0532351B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a process for producing polycrystalline aluminum nitride products that are phase-pure and have a thermal conductivity greater than 0.5 W/cm·K at 22°C. A reasonably pure aluminum nitride single crystal containing 300 ppm dissolved oxygen is known to have a thermal conductivity of 2.8 W/cm K at room temperature;
The thermal conductivity is almost the same as that of BeO single crystal (3.7 W/cm·K), and it is also slightly higher than the thermal conductivity of α-Al ₂ O ₃ single crystal (0.44 W/cm·K). The thermal conductivity of aluminum nitride single crystals is highly dependent on the dissolved oxygen content, and it decreases as the dissolved oxygen content increases. For example, the thermal conductivity of an aluminum nitride single crystal containing 0.8% (by weight) of dissolved oxygen is approximately 0.8 W/cm·K. Aluminum nitride has a strong affinity for oxygen. When oxygen is introduced into the aluminum nitride lattice of the aluminum nitride powder, Al vacancies are generated according to the reaction equation 3N ^-3 →30 ^-2 +V (N ^-3 ) (N ^-3 ) (Al ⁺³ ). That is, if three oxygen atoms are inserted into three nitrogen positions, one vacancy will be created at the aluminum position.
The presence of oxygen atoms at nitrogen positions probably has a negligible effect on the thermal conductivity of aluminum nitride. However, since the mass difference between aluminum atoms and vacancies is large, the presence of vacancies at aluminum positions has a strong influence on the thermal conductivity of aluminum nitride.For practical purposes, the thermal conductivity of aluminum nitride is probably It seems that all of the decrease in Typically, there are three sources of oxygen present in aluminum nitride powder. The first source is the discrete state
They are _{Al2O3 particles} . The second source is an oxide coating (possibly
Al ₂ O ₃ coating). The third source is oxygen dissolved in the aluminum nitride lattice. The amount of oxygen present in the aluminum nitride lattice of aluminum nitride powder depends on the method of manufacturing the aluminum nitride powder. Furthermore, heating the aluminum nitride powder at high temperatures may also introduce oxygen into the aluminum nitride lattice. Measurements have shown that at a temperature of about 1900° C., aluminum nitride lattice can dissolve about 1.2% (by weight) of oxygen. The use of free carbon in accordance with the present invention allows the removal of the oxygen present in the aluminum nitride powder as first and second sources, and possibly also some of the oxygen as a third source. be able to. Briefly stated, the present invention utilizes free carbon to deoxidize aluminum nitride powder to reduce the
% and up to about 1.1% (by weight), and then by pressureless sintering of a compacted body of the resulting deoxidized powder, greater than 85% of its theoretical density. density, oxygen content greater than 0.35% (by weight) and up to approximately 1.1% (by weight) based on the weight of the sintered body, and 0.5 W/cm at 22°C.
The present invention relates to a method for producing a polycrystalline aluminum nitride sintered body having a thermal conductivity greater than K. In the present invention, oxygen content can be measured by neutron activation analysis. Pressureless sintering here refers to compressed or compacted bodies made of the deoxygenated aluminum nitride of the present invention under ambient pressure (that is, without applying mechanical pressure).
By densification or bonding it is meant to obtain a ceramic product with a density greater than 85% of the theoretical density. The thermal conductivities mentioned for the sintered bodies of the invention are values at approximately 22°C. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more clearly and better understood by those skilled in the art upon consideration of the following detailed description in conjunction with the accompanying drawings. Briefly, according to one embodiment of deoxidizing bulk powder, a density greater than 85% of the theoretical density of aluminum nitride and 0.5 W/cm.
The method of the present invention for producing a sintered body having a thermal conductivity greater than K includes (1)(a) a predetermined amount of 0.8% (by weight), preferably greater than 0.9% (by weight), based on the weight of aluminum nitride; Oxygen content and approx. 4.7
Aluminum nitride having a specific surface area greater than about 40 m ² /g and (b) free carbon having ^a specific surface area greater than about 40 m 2 /g and pyrolyzed at a temperature within the range of about 50 to 1000° C. to form free carbon and volatility. and a carbonaceous additive selected from the group consisting of carbon-containing organic substances producing gaseous decomposition products of Approximately 0.35 (weight)% based on
and up to about 1.1% (by weight) while being at least about 20% (by weight) less than the predetermined oxygen content above. providing an at least substantially homogeneous granular mixture such that
The particulate mixture described above is heated in a non-oxidizing atmosphere selected from the group consisting of argon, nitrogen and mixtures thereof to a temperature within the range of about 1350°C to about 1750°C; particulate by pyrolyzing it to produce free carbon and reacting the free carbon in the particulate mixture with the oxygen contained in the aluminum nitride to produce a deoxidizing powder and a volatile gaseous product. The mixture is deoxidized; the deoxidized powder is molded into a compressed body; the oxygen content of the compressed body is then reduced to its approximately 1900 to approximately 1900 to approximately 0.35% (by weight) of weight
It consists of the steps of sintering the compressed body into a sintered body at a temperature in the range of 2200°C and under ambient pressure, and is characterized in that the above oxygen content can be measured by neutron activation analysis. It is something to do. Briefly, according to another embodiment of deoxidizing a compressed body, a density greater than 85% of the theoretical density of aluminum nitride and 0.5 W/cm K
The method of the present invention for producing a sintered body having a higher thermal conductivity comprises: (1)(a) a predetermined amount of 0.8% (by weight), preferably greater than 0.9% (by weight), based on the weight of aluminum nitride; Oxygen content and approx. 4.7
Aluminum nitride having a specific surface area greater than about 40 m ² /g and (b) free carbon having ^a specific surface area greater than about 40 m 2 /g and pyrolyzed at a temperature within the range of about 50 to 1000° C. to form free carbon and volatility. and a carbonaceous additive selected from the group consisting of carbon-containing organic substances producing gaseous decomposition products of Approximately 0.35 (weight) based on weight
% and up to about 1.1% (by weight) while being less than the predetermined oxygen content by at least about 20% (by weight). providing an at least substantially homogeneous granular mixture present in a suitable amount; (2) forming said granular mixture into a compressed body; heating the compacted body in a non-oxidizing atmosphere to a temperature within a range from about 1350°C to a temperature at which the pores of the compacted body are kept open;
If organic substances exist in the compressed body, they are thermally decomposed to generate free carbon, and the free carbon in the compressed body is reacted with oxygen contained in aluminum nitride to form a deoxygenated compressed body and volatile (4) deoxygenating the compressed body by producing a gaseous product; and then (4) reducing the oxygen content of the compressed body in a non-oxidizing atmosphere selected from the group consisting of argon, nitrogen, and mixtures thereof. sintering the compressed body into a sintered body at a temperature within the range of about 1900 to about 2200°C and under ambient pressure while maintaining a value greater than about 0.35% (by weight) of The above-mentioned oxygen content is characterized in that it can be measured by neutron activation analysis. The aluminum nitride powder used in the method of the present invention may be of commercial or industrial grade. Specifically, such aluminum nitride must be free of impurities that would significantly adversely affect the desired properties of the resulting sintered body, and must have a purity of at least about 99%, excluding oxygen. It is preferable. Typically, commercially available aluminum nitride contains about 1.5% to about 3% (by weight) oxygen. Note that the oxygen content of aluminum nitride can be measured by neutron activation analysis. The aluminum nitride powder for use in the present invention has a surface area of approximately 4.7 m ² /g as measured according to the BET surface area measurement method.
having a larger specific surface area, preferably about 5.0~
It has a specific surface area of about 12 m ² /g. As defined via specific surface area, it has an average equivalent particle size of less than about 0.39μ, preferably from about 0.37 to about 0.15μ
It has an average equivalent particle size of Aluminum nitride powder having a specific surface area of less than about 4.7 m ² /g is difficult to sinter in the present invention and is not practically useful. The free carbon for the present invention generally has a specific surface area of greater than 40 m ² /g, preferably greater than 150 m ² /g, as measured according to the BET surface area measurement method. In terms of particle size, the free carbon for the present invention has an average equivalent particle size of less than 0.09μ, preferably less than 0.024μ. Note that the free carbon is most preferably as fine as possible so that the deoxygenated aluminum nitride of the present invention is produced by intimate contact with the aluminum nitride powder. Powdered free carbon can be mixed with aluminum nitride powder by various conventional methods (eg, ball milling in a dispersion). In addition,
Preferably, the particulate free carbon is graphite. The carbon-containing organic material can be mixed with the aluminum nitride powder by various conventional methods. Elemental carbon and volatile gaseous decomposition products are then produced by pyrolysis of the organic material in the aluminum nitride powder or compact. Thermal decomposition of organic materials is carried out at temperatures within the range of about 50 to about 1000°C and under ambient pressure. Such pyrolysis must also be carried out in a non-oxidizing atmosphere (such as argon or nitrogen) which does not adversely affect it, most preferably in nitrogen. The actual amount of free carbon introduced by pyrolysis of the organic material can be determined by pyrolyzing only the organic material and measuring the weight loss. The thermal decomposition of the organic substance in the compressed body is preferably carried out in a sintering furnace while raising the temperature to the deoxidation temperature (that is, the temperature at which the generated free carbon reacts with the oxidation contained in the aluminum nitride). Specifically, if the organic substance is solid,
Preferably, it is mixed in solution to coat the aluminum nitride particles. The wet mixture may then be processed to remove the solvent and the resulting dry mixture may be heated to decompose the organic material and produce free carbon before forming the mixture into a compact. If desired, the wet mixture may be formed into a compact before the solvent is removed. Removal of the solvent can be accomplished by various methods such as evaporation or lyophilization (ie sublimation of the solvent from the frozen dispersion in vacuo). Similarly, if the organic material is a liquid, it can be mixed with the aluminum nitride powder and then heated to pyrolyze the organic material to produce free carbon by heating the wet mixture. Or again,
After the wet mixture is formed into a compressed body, the compressed body may be heated to thermally decompose the organic material and generate free carbon in situ, while at the same time volatilizing the gaseous decomposition products. If you do this,
A substantially uniform coating of organic material is obtained on the aluminum nitride particles, thus resulting in the production of substantially uniformly distributed free carbon upon pyrolysis. As the carbon-containing organic material for producing the free carbon additive of the present invention, high molecular weight aromatic compounds are preferred because, upon pyrolysis, particulate free carbon, typically of submicron size, is produced in the required yield. be. Examples of such aromatic compounds include phenol formaldehyde condensation resins (known as novolaks) which are soluble in acetone or higher alcohols (e.g. butyl alcohol) and many related condensation resins such as resorcinol formaldehyde resins, aniline formaldehyde resins, etc. resins and cresol formaldehyde resins. Another satisfactory group of organic substances are derivatives of polynuclear aromatic hydrocarbons (eg dibenzanthracene and chrysene) contained in coal tar. Polymers of aromatic hydrocarbons that are soluble in aromatic hydrocarbons, such as polyphenylene and polymethylphenylene, are also suitable organic substances. In the deoxidation step of the present invention, most of the free carbon reacts with the oxygen contained in the aluminum nitride to produce volatile carbon monoxide gas. In this case, it is believed that the following deoxidizing reaction occurs. In addition, in the formula, the oxygen contained in aluminum nitride is shown as Al ₂ O ₃ . Al ₂ O ₃ +3C → 2Al (liquid) + 3CO (gas) (1) Al ₂ O ₃ +2C → 2CO (liquid) + Al ₂ O (gas) (2) Gaseous carbon-containing products in any deoxidation reaction is produced, and its volatilization removes free carbon. Also, small amounts of free carbon, typically less than about 0.1% (by weight), may be dissolved in the aluminum nitride. Furthermore, small amounts of free carbon may undergo reactions such as those described below. C+AlN→AlCN (gas) (3) In the deoxidation step of the present invention, free carbon must be used in an amount suitable for producing the deoxidized powder or compressed body of the present invention. Specifically, the amount of free carbon used is a deoxidizing powder having an oxygen content greater than about 0.35% (by weight) and up to about 1.1% (by weight) based on the weight of the deoxidizing powder or compact. or a compacted body, and the oxygen content must be at least about 20% (by weight) less than the predetermined oxygen content of the aluminum nitride feedstock. When the oxygen content is about 0.35% (by weight) or less,
A product of sufficiently high density cannot be obtained. In other words, the sintered body of the present invention having a density greater than 85% of the theoretical density of aluminum nitride cannot be obtained.
For a given system, as the oxygen content increases, the density of the resulting sintered body increases, but its thermal conductivity decreases. The amount of free carbon used is 0.8% (by weight) based on the weight of the deoxidizing powder.
and up to about 1.1% (by weight) to produce a deoxidized powder. Similarly, the amount of free carbon used produces a deoxygenated compact having an oxygen content greater than about 0.5% (by weight) and up to about 0.9% (by weight) based on the weight of the deoxygenated compact. It is preferable that the
% (by weight) and up to about 0.9% (by weight). The amount of free carbon remaining in the deoxidized powder or compacted body must not cause the compacted body to be deoxidized to the extent that it prevents the achievement of the densities of the present invention; The amount should be less than about 0.2% (by weight) based on the weight of the deoxygenated compact. More specifically, it is necessary to maintain the oxygen content of the deoxygenated compact during sintering at a value greater than 0.35% (by weight). The amount of free carbon required to produce the deoxidized powder or compact of the present invention can be determined experimentally. For example, on a given aluminum nitride with a given oxygen content, a series of deoxidizing operations with stepwise increasing amounts of free carbon are carried out, and the oxygen content of each resulting deoxidized powder or compact is determined by neutrons. It can be measured by activation analysis. However, it is preferable to calculate an initial approximation amount consisting of a theoretical amount of carbon shown in reaction equation (1) from reaction equation (1), and to conduct an experiment using such an approximation amount. The amount of free carbon required to produce the deoxidized powder or compact of the present invention is then determined by performing one or more deoxidation operations on a given aluminum nitride. The deoxidizing operation in the present invention is performed by heating the mixture of aluminum nitride and free carbon to the deoxidizing temperature to react the free carbon with the oxygen content in the aluminum nitride. It consists of generating a body. Most preferably, such deoxygenation operations are carried out under ambient pressure in a non-oxidizing atmosphere selected from the group consisting of argon, nitrogen and mixtures thereof, and especially in nitrogen. Generally speaking, the deoxygenation time will vary from about 1/4 to about 2 hours depending on the deoxygenation temperature, particle size, and homogeneity of the aluminum nitride and free carbon mixture.
That is, the higher the deoxidation temperature, the smaller the particle size, and the more homogeneous the mixture, the shorter the deoxidation time. According to one embodiment, the powder comprising a mixture of aluminum nitride and free carbon is heated to about 1350 to about 1750
The powder is deoxidized by heating to a temperature in the range of 0.degree. C., preferably about 1600.degree. C., to cause the free carbon to react with the oxygen contained in the aluminum nitride.
Temperatures below 1350°C are impractical as they require long times, and temperatures above about 1750°C will cause the powder to coagulate. According to another embodiment, the compressed body of aluminum nitride and free carbon is heated from 1350°C to a temperature at which the pores of the compressed body remain open (generally about 1800°C).
The deoxygenated compact according to the invention is obtained by heating to a temperature in the range up to 1600°C, preferably about 1600°C. Note that it is preferable to deoxidize the compressed body by holding the compressed body at a deoxidizing temperature for a required period of time in a sintering furnace, and then increasing the temperature to the sintering temperature. Deoxidation of the compact must be completed before the pores of the compact are closed by sintering. Otherwise, the sintered body of the present invention cannot be obtained because the volatilization of the gaseous products is hindered. Various methods can be used to form the particulate mixture into a compact. For example, a compressed body of a desired shape can be obtained by extrusion, injection molding, mold compression, isostatic compression or slip casting. Lubricants, binders or similar additives used to aid in shaping the mixture must not have a significant adverse effect on the compacted body or the sintered body of the present invention. Preferably, such forming aids are such that they evaporate leaving little residue when heated to relatively low temperatures, preferably below 200°C. In addition, in order to promote high density during sintering, the compacted body has a density equal to at least about 40% of the theoretical density of aluminum nitride, preferably 50%.
It is necessary to have a density greater than %. Additional oxygen losses also occur during heating of the deoxygenated compact to sintering temperature and during sintering, the amount of which is highly dependent on the heating rate, sintering temperature, and rate of densification of the compact. For example, the higher the open porosity of the compact at temperatures above 1600° C., and the lower the heating rate to the sintering temperature, the greater the amount of oxygen loss. In the present invention, during the sintering operation to obtain the sintered body of the present invention, the oxygen content of the deoxidized compact is approximately 0.35% of its weight.
(wt)% greater than preferably about 0.4 (wt)
It is necessary to keep it at a value greater than %. The deoxygenated compact is sintered at a temperature within the range of about 1900°C to about 2200°C, preferably about 2050°C. At temperatures below about 1900° C., sintered bodies of the invention with densities greater than 85% of the theoretical density cannot be obtained. On the other hand, about
Aluminum nitride easily decomposes at temperatures higher than 2200°C. The sintering temperature necessary to obtain the sintered body of the invention can be determined experimentally, but it is highly dependent on the surface area of the aluminum nitride, the density of the compact and the oxygen content of the aluminum nitride.
Specifically, the larger the surface area of the aluminum nitride, i.e. the smaller the grain size, the lower the required sintering temperature. Furthermore, the higher the density of the compressed body, the lower the required sintering temperature. Furthermore, the higher the oxygen content, the lower the required sintering temperature. Sintering times can be determined experimentally. Typically, the sintering time at about 2050°C is about 1 hour. Sintering of the deoxygenated compact is carried out under ambient pressure in an atmosphere selected from the group consisting of argon, nitrogen and mixtures thereof. Note that, regardless of whether or not the compressed body has been deoxidized, it is preferable to embed the compressed body in aluminum nitride powder prior to sintering. This is to prevent weight loss due to decomposition of aluminum nitride during sintering at temperatures above about 1950°C. The polycrystalline material of the present invention is a pressureless sintered ceramic product. It is made of aluminum nitride and is approximately 0.35 (weight) based on the weight of it
% and up to about 1.1% (by weight) of oxygen. Incidentally, the higher the oxygen content, the higher the density can be achieved, so the sintered body of the present invention has an oxygen content of more than about 0.4% (by weight) and up to about 0.9% (by weight) based on the weight of the sintered body. of oxygen, and also about 0.55 (by weight)
% and up to about 0.8% (by weight) of oxygen are most preferred. The sintered bodies of the present invention also contain detectable amounts of carbon in some form up to less than about 0.2% (by weight). The sintered body of the present invention is phase-pure,
Or it does not contain substantial amounts of other phases. The expression "does not contain a substantial amount of other phases" as used herein means that the total amount of other phases present in the sintered body of the present invention is less than about 1% (by volume) based on the volume of the sintered body. do. The sintered bodies of the present invention have a density greater than 85% of the theoretical density of aluminum nitride. Generally speaking it has a density greater than 90% and preferably greater than 95% of the theoretical density of aluminum nitride. According to the invention, complex shapes and/or
It becomes possible to directly manufacture hollow-shaped polycrystalline aluminum nitride ceramic products. In particular, the ceramic products of the present invention can be manufactured in complex shapes such as impermeable crucibles, thin-walled tubes, long rods, spheres, or hollow articles without machining. Note that the dimensions of the ceramic product of the present invention differ from the dimensions of the green body by the shrinkage (ie, densification) that occurs during sintering. The ceramic products of the present invention have a variety of uses. It is particularly useful as a substrate for integrated circuits, especially silicon semiconductor chips for use in computers. The ceramic products of the present invention are also useful as sheathing materials for temperature sensors and components that come into contact with hot liquid aluminum. Because the ceramic products of the present invention consist of only a single phase and do not contain substantial amounts of other phases, they are less chemically reactive toward certain substances. In the present invention, unless otherwise specified, the density of the sintered body and the unsintered body is expressed as a percentage of the theoretical density of aluminum nitride (3.261 g/cm ³ ). In order to explain the present invention in more detail, examples are shown below. In these examples, the following operating procedures were used unless otherwise noted. Standard commercially available aluminum nitride powder with a purity of 99.8% excluding oxygen was used. The powder had an oxygen content of 1.97% (by weight) based on its weight and a surface area of 5.25 m ² /g.
The analytical results presented by the supplier were as follows. Individual analysis results N=33% C=150ppm Spectral analysis results Cu=0.0005~0.005% Mn=0.001% Fe=0.001~0.01% Mg=0.0005~0.005% Si=0.0005~0.005% Before use, add aluminum nitride powder. It was placed in a glass flask and stored in a glove box filled with _N2 . The graphite used has a specific surface area of 200 m ² /g or
It had an average particle size of 0.018. The graphite was previously heated in nitrogen at 900° C. for 1 hour to remove volatile substances such as moisture. Oxygen content was determined by neutron activation analysis. The phase composition of the sintered body was examined by optical microscopy and X-ray diffraction analysis. After compaction, the green sample (ie, the compact) measured approximately 0.4 inches in diameter and 0.2-0.3 inches in length. The compact was heated in a furnace at a rate of about 120°C/min. The thermal conductivity of the sintered body was measured by a steady heat flow method using a rod-shaped test piece cut from the sintered body.
This method was originally invented in 1888 by A. Berget.
In a paper by GASlack published in "Encyclopaedic Dictionary of Physics" edited by J. Thewlis (Pergamon Publishing, Oxford, 1961) Are listed. According to this method, a test specimen is placed inside a high vacuum chamber, heat is supplied to one end by an electric heater, and the temperature is measured by a fine wire thermocouple. The specimen is surrounded by a protective cylinder with a matched temperature gradient. Absolute accuracy is ±5%. For comparison, using the same equipment
When the thermal conductivity of Al ₂ O ₃ single crystal was measured, it was approximately 22
It was 0.44W/cm・K at ℃. Example 1 0.115 g of graphite was added to 10 g of aluminum nitride powder. The mixture was placed in a plastic jar with aluminum nitride grinding media and heptane and subjected to vibratory milling for 24 hours at room temperature. The dispersion thus obtained was poured into a flask and dried at 50-200°C in a vacuum of about 200 Torr. After vacuum drying, the flask was filled with _N2 . Therefore, the samples were not exposed to oxygen during drying. During the vibratory milling process, a portion of the aluminum nitride grinding media was abraded, and the amount was found to be 0.413 g. As a result, the resulting dry powder mixture contained 1.09% (by weight) graphite based on its weight. The flask containing the dried mixture was placed in a glove box filled with _N2 . A portion of the mixture was charged into a mold within the box, then removed from the box and mold compacted at room temperature and under a pressure of 10 Kpsi. After repositioning the mold in a glove box filled with N ₂ , the resulting black pellets (i.e. compacts) were removed and inserted into a molybdenum boat. In this case, the pellets were embedded in a mixture having the same composition as the pellets, namely aluminum nitride powder and 1.09% (by weight) graphite. After the boat was covered with a molybdenum lid, it was placed in a flask filled with N ₂ and then transferred into a molybdenum-lined furnace and then heated to 1550° C. under ambient pressure in a nitrogen atmosphere. to 1550℃
After keeping it for 60 minutes, raise the temperature to 1600℃ and keep it at that temperature for 30 minutes.
I kept it for a minute. Next, the temperature was raised to a sintering temperature of 2060° C., maintained at that temperature for 70 minutes, and then cooled in a furnace to room temperature in a nitrogen atmosphere. The sintered body thus obtained is gray in color and has a 4.45
% weight loss. This indicates that most of the graphite has reacted and been removed as a carbon-containing gaseous product. The sintered body had a density equal to 90.6% of the theoretical density of aluminum nitride. It was also phase-pure and had an oxygen content of 0.42% (by weight) based on its weight. Its resistivity at room temperature (ie about 22° C.) was measured to be 4×10 ¹⁴ Ω·cm under a voltage of 100V and 8×10 ¹² Ω·cm under a voltage of 1000V. This example is shown in Table 1. All of the examples shown in Table 1 were performed in substantially the same manner except as noted in the table and below. Specifically, in Examples 1A, 1B, 2-14, and 23, the vibratory milled dispersions of aluminum nitride and graphite were dried as in Example 1. However, Examples 15 to 22
In , the vibratory milled dispersion was dried in air under a heat lamp for 1 hour. Due to this drying in air, the granular mixture absorbed excess oxygen. The graphite content given in Table 1 is the amount present in the granular mixture after vibratory milling and drying. In Examples 1A, 1B, 2-14 and 23,
After drying, the granular mixture was mold compacted at room temperature and under the indicated pressure. In Examples 9 and 15-22, the granular mixture was first heated to room temperature and about 5 kpsi.
The resulting pellets were then isostatically compressed at room temperature and the pressures listed in Table 1. In Examples 1A, 1B, 2-14, 21 and 23, prior to deoxidation or deoxidation and sintering,
The compact was embedded in a mixture of aluminum nitride powder and graphite having the same composition as the compact. Example
Nos. 15-20 and 22 did not embed the compact in aluminum nitride powder or any other powder. All of the heat treatments (i.e. deoxidation or deoxidation and sintering) in Table 1, except for Example 1B,
It was carried out under ambient pressure in a nitrogen atmosphere.
Specifically, the nitrogen flow rate in Example 15 was approximately 2 cubic feet per hour, and (Example 1B)
The nitrogen flow rate in the other examples (excluding 100 ft/hr) was about 0.1 cubic feet/hour. With the exception of Example 1B, all samples after heat treatment were cooled in a furnace to approximately room temperature in a nitrogen atmosphere. Example
In 1B, deoxidation and sintering of the compacts was carried out under ambient pressure in argon. The flow rate of argon was about 0.1 cubic feet per hour, and the heat-treated samples were cooled in the furnace to about room temperature in argon. Examples 1A, 1B, 5, 8, 9, 11, 14 and 19
The heat treatment in ~21 was almost the same as in Example 1 except for the points described in the table and text. Examples 2 and 4 were the same as Example 1 except as noted in the table and that the compact was deoxidized while being heated to the sintering temperature at a rate of about 120°C/min. It was carried out in almost the same way. Example 22 is
It was carried out in substantially the same manner as in Example 2 except that graphite was not contained and the points listed in the table. Examples 3, 6, 7, 10, 12, 13 and 15-18
Example 1 was carried out in substantially the same manner as in Example 1, except that the compressed body was not sintered and the points stated in the table and text. In Examples 1, 1A, 1B, and 2 to 21, compressed bodies made of aluminum nitride and graphite were deoxidized. However, in Example 23, the black granular mixture obtained after vibratory milling and drying was placed in a tube furnace made of Al ₂ O ₃ and then heated to 1550° C. under ambient pressure in nitrogen; It was held at that temperature for 60 minutes and then cooled in the furnace under nitrogen to about room temperature. The aluminum nitride powder thus deoxidized is gray in color and 3.17% (by weight)
showed a decrease in weight. This indicates that a substantial amount of graphite has reacted and been removed as a carbon-containing gaseous product. Such deoxidizing powder is
It had an oxygen content of 0.53% (by weight). Chemical analysis of a portion of the oxygen absorbing powder revealed that it was 0.276 (by weight)
It was found to contain % oxygen. In Example 23, a portion of the deoxidized powder was compressed with a mold at room temperature, and the resulting compressed body was sintered at 2050° C. for 60 minutes. The densification of the compressed body in Example 23 is as follows:
The residual carbon caused additional deoxidation of the aluminum nitride, which was hampered by the oxygen content becoming too low. The relative densities shown in Table 1 are percentages of the theoretical density of aluminum nitride (3.261 g/cc). Examples 1, 2, 4, 5, 8, 11, 14 and 20~
22 indicates the oxygen content and/or carbon content of the sintered body, whereas the other examples indicate the oxygen content and/or carbon content of the deoxygenated compact. Note that the oxygen content and carbon content are expressed as a percentage of the weight of the deoxygenated compressed body or sintered body. The thermal conductivities and resistivities shown in Table 1 are values for sintered bodies. Note that the thermal conductivity and resistivity were measured at room temperature (about 22°C).

【table】

[Table] In Table 1, Examples 1, 1A, 1B, 2 and 19~
21 illustrates the production of the sintered body of the present invention. Specifically, when comparing the thermal conductivity and oxygen content of Examples 1, 20, and 21 with the oxygen content of Example 2 based on other research results, it is found that
It can be seen that the sintered bodies of 1A, 1B and 2 should have a thermal conductivity of at least about 0.7 W/cm·K at about 22°C. Also, if we compare Example 19 with Examples 20 and 21, the sintered body of Example 19 should have an oxygen content greater than 0.4% (by weight) and less than 0.9% (by weight), and it should have an oxygen content of at least Approx. 0.55W/cm・
It can be seen that it should have a thermal conductivity of K.
Furthermore, a comparison of Example 19 with Examples 20 and 21 shows that the sintered body of Example 19 should have a resistivity greater than 10 ¹¹ at 22° C. and under a voltage of 100V. In the accompanying drawings, a cross section of the sintered body of Example 21 obtained after being polished but not corroded is shown. The large black dots in the figure are traces caused by polishing. As can be seen from the drawings, it can be seen that the sintered bodies of the present invention have a substantially uniform microstructure, and the grains have a relatively equiaxed morphology and a relatively uniform grain size. The figures also show that the microstructure consists of only a single phase and does not contain substantial amounts of other phases. The sintered bodies of Examples 1, 1A, 1B, 2 and 19-21 have various uses. Among these, they are particularly useful as substrates for electronic circuits. Particularly dense products are also useful as crucibles for certain metals and alloys (eg, aluminum). Example 3 in Table 1 illustrates the deoxidation of the compact and shows the amount of carbon present in the deoxygenated compact of Example 1. Comparing Examples 4-8, Examples 7 and 8
It can be seen that high losses during heating at 2050°C impede densification, as shown by the oxygen content of . A comparison of Examples 9 to 14 shows that the presence of an excessive amount of carbon in the compact relative to the amount of oxygen prevents its densification, and that Examples 13 and 14
It can be seen that additional deoxygenation occurs at temperatures above 1600°C, as indicated by the oxygen content of . Because the dispersions of Examples 4-8 were not exposed to oxygen during drying, the oxygen content of the resulting dry granular mixtures was lower than that of Examples 18-8, which were dried in air.
The oxygen content was significantly lower than that of the granular mixture of 21. Examples 15-17 show that weight loss increases with increasing deoxygenation temperature. Example 18 shows the amount of carbon present in the deoxygenated compacts of Examples 19-21. Since no graphite was used in Example 22, the sintered body had a low thermal conductivity and contained other phases occupying about 10% (by volume) of its volume. In Example 23, densification of the compact during sintering was limited due to additional deoxidation provided by residual carbon.

[Brief explanation of the drawing]

The drawing shows 97.2% of the theoretical density of aluminum nitride
1 is a micrograph (magnification: 750X) showing the metal structure of a polished cross section of a sintered body of the present invention having a density equal to .

Claims (1)

[Claims] 1 Approximately based on the weight of granular aluminum nitride
A granular mixture comprising aluminum nitride having a predetermined oxygen content greater than 0.8% (by weight) and a carbonaceous additive selected from the group consisting of free carbon, carbon-containing organic substances and mixtures thereof, the carbon-containing organic The substance thermally decomposes at temperatures in the range of about 50 to 1000°C to produce free carbon and volatile gaseous decomposition products; aluminum nitride has a specific surface area greater than about 4.7 m ² /g; providing at least a substantially homogeneous granular mixture of carbon having a specific surface area greater than about 40 m ² /g; 1350~approx. 1750
℃ to pyrolyze the organic material, if present, in the particulate mixture to produce free carbon, and convert the free carbon in the particulate mixture to the oxygen contained in the aluminum nitride. The particulate mixture is deoxidized by reacting with a deoxidizing powder to form a volatile gaseous product, and the particulate mixture is deoxidized by reacting with a deoxidizing powder and a volatile gaseous product to form a deoxidizing powder of about 0.35 (by weight) based on the weight of the deoxidizing powder.
% and up to about 1.1% (by weight) while being less than said predetermined oxygen content by at least about 20% (by weight). the deoxidized powder is compacted into a compact, and the oxygen content of the compact is reduced to that level in a non-oxidizing atmosphere selected from the group consisting of argon, nitrogen and mixtures thereof. Approximately 0.35 of the weight of
(weight)% while keeping it greater than about 1900~
sintering said compressed body into a sintered body at a temperature in the range of about 2200° C. and under ambient pressure, said oxygen content being measurable by neutron activation analysis. made by a method characterized and consisting essentially of an aluminum nitride phase with a particle size of about 0.35 as determined by neutron activation analysis.
(by weight)% and up to about 1.1% (by weight), ranging from detectable amounts to about 1.1% (by weight).
containing carbon in amounts ranging up to less than 0.2% (by weight);
and polycrystalline aluminum nitride products having a density greater than 85% of the theoretical density of aluminum nitride and a thermal conductivity greater than 0.5 W/cm·K at 22°C. 2 Approximately based on the weight of granular aluminum nitride
A granular mixture comprising aluminum nitride having a predetermined oxygen content greater than 0.8% (by weight) and a carbonaceous additive selected from the group consisting of free carbon, carbon-containing organic substances and mixtures thereof, the carbon-containing organic The substance thermally decomposes at temperatures in the range of about 50 to 1000°C to produce free carbon and volatile gaseous decomposition products; aluminum nitride has a specific surface area greater than about 4.7 m ² /g; providing an at least substantially homogeneous granular mixture having a specific surface area greater than about 40 m ² /g; forming the granular mixture into a compact; carbon selected from the group consisting of argon, nitrogen and mixtures thereof; The compacted body is heated in a non-oxidizing atmosphere to a temperature within the range of about 1350° C. to a temperature at which the pores of the compacted body remain open, and any organic material, if any, is present in the compacted body. by pyrolyzing to produce free carbon, and reacting the free carbon in the compressed body with the oxygen contained in the aluminum nitride to produce a deoxygenated compressed body and a volatile gaseous product. The compressed body is deoxidized, and the oxygen content exceeds about 0.35% (by weight) and about 1.1% (by weight) based on the weight of the deoxidized compressed body.
% and at the same time less than the predetermined oxygen content by at least about 20% (by weight); The compressed body is then heated in a non-oxidizing atmosphere selected from the group consisting of argon, nitrogen and mixtures thereof, while maintaining the oxygen content of the compressed body at a value of greater than about 0.35% (by weight) of its weight. sintering the deoxygenated compact into a sintered body at a temperature in the range of 2200°C and under ambient pressure, the oxygen content being measurable by neutron activation analysis. made by the method characterized and consisting essentially of an aluminum nitride phase ranging from greater than about 0.35% (by weight) to about 1.1% (by weight) as determined by neutron activation analysis. containing an amount of oxygen, containing an amount of carbon ranging from a detectable amount to less than about 0.2% (by weight), and having a density greater than 85% of the theoretical density of aluminum nitride and at 22°C.
Polycrystalline aluminum nitride products with thermal conductivity greater than 0.5W/cm・K. 3 Approximately based on the weight of granular aluminum nitride
A granular mixture comprising aluminum nitride having a predetermined oxygen content greater than 0.8% (by weight) and a carbonaceous additive selected from the group consisting of free carbon, carbon-containing organic substances and mixtures thereof, the carbon-containing organic The substance thermally decomposes at temperatures in the range of about 50 to 1000°C to produce free carbon and volatile gaseous decomposition products; aluminum nitride has a specific surface area greater than about 4.7 m ² /g; providing at least a substantially homogeneous granular mixture of carbon having a specific surface area greater than about 40 m ² /g; 1350~approx. 1750
℃ to pyrolyze the organic material, if present, in the particulate mixture to produce free carbon, and convert the free carbon in the particulate mixture to the oxygen contained in the aluminum nitride. The particulate mixture is deoxidized by reacting with a deoxidizing powder to form a volatile gaseous product, about 0.8 (by weight) based on the weight of the deoxidizing powder.
% and up to about 1.1% (by weight) while being less than said predetermined oxygen content by at least about 20% (by weight). the deoxidized powder is compacted into a compact, and the oxygen content of the compact is reduced to that level in a non-oxidizing atmosphere selected from the group consisting of argon, nitrogen and mixtures thereof. Approximately 0.4 of the weight of
(weight)% while keeping it greater than about 1900~
sintering said compressed body into a sintered body at a temperature in the range of about 2200° C. and under ambient pressure, said oxygen content being measurable by neutron activation analysis. made by a method characterized and consisting essentially of an aluminum nitride phase, with a particle size of about 0.40 as determined by neutron activation analysis.
(by weight)% and up to about 0.9% (by weight), ranging from detectable amounts to about 0.9% (by weight).
containing carbon in amounts ranging up to less than 0.2% (by weight);
and a polycrystalline aluminum nitride product according to claim 1, having a density greater than 85% of the theoretical density of aluminum nitride and a thermal conductivity greater than 0.5 W/cm·K at 22°C. 4 Approximately based on the weight of granular aluminum nitride
A granular mixture comprising aluminum nitride having a predetermined oxygen content greater than 0.8% (by weight) and a carbonaceous additive selected from the group consisting of free carbon, carbon-containing organic substances and mixtures thereof, the carbon-containing organic The substance thermally decomposes at temperatures in the range of about 50 to 1000°C to produce free carbon and volatile gaseous decomposition products; aluminum nitride has a specific surface area greater than about 4.7 m ² /g; providing an at least substantially homogeneous granular mixture having a specific surface area greater than about 40 m ² /g; forming the granular mixture into a compact; carbon selected from the group consisting of argon, nitrogen and mixtures thereof; The compacted body is heated in a non-oxidizing atmosphere to a temperature within the range of about 1350° C. to a temperature at which the pores of the compacted body remain open, and any organic material, if any, is present in the compacted body. by pyrolyzing to produce free carbon, and reacting the free carbon in the compressed body with the oxygen contained in the aluminum nitride to produce a deoxygenated compressed body and a volatile gaseous product. The compressed body is deoxidized, and the oxygen content exceeds about 0.50 (by weight) and about 0.9 (by weight) based on the weight of the deoxidized compressed body.
% and at the same time less than the predetermined oxygen content by at least about 20% (by weight); The compressed body is then heated in a non-oxidizing atmosphere selected from the group consisting of argon, nitrogen and mixtures thereof, while maintaining the oxygen content of the compact at a value of greater than about 0.4% (by weight) of its weight. sintering the deoxygenated compact into a sintered body at a temperature in the range of 2200°C and under ambient pressure, the oxygen content being measurable by neutron activation analysis. made by the method characterized, consisting essentially of an aluminum nitride phase ranging from greater than about 0.40% (by weight) to about 0.9% (by weight) as determined by neutron activation analysis. containing an amount of oxygen, containing an amount of carbon ranging from a detectable amount to less than about 0.2% (by weight), and having a density greater than 85% of the theoretical density of aluminum nitride and at 22°C.
A polycrystalline aluminum nitride product according to claim 2 having a thermal conductivity greater than 0.5 W/cm·K. 5. The polycrystalline aluminum nitride product according to claim 1, wherein the atmosphere is nitrogen. 6. The polycrystalline aluminum nitride product according to claim 1, having a density greater than 90% of the theoretical density of aluminum nitride. 7. The polycrystalline aluminum nitride product according to claim 1, having a density greater than 95% of the theoretical density of aluminum nitride. 8. The polycrystalline aluminum nitride product according to claim 2, wherein the atmosphere is nitrogen. 9. The polycrystalline aluminum nitride product according to claim 2, having a density greater than 90% of the theoretical density of aluminum nitride. 10 Density is 95% of the theoretical density of aluminum nitride
A polycrystalline aluminum nitride product according to claim 2 of the larger claim. 11. The polycrystalline aluminum nitride product according to claim 3, wherein the atmosphere is nitrogen. 12 Density is 90% of the theoretical density of aluminum nitride
A polycrystalline aluminum nitride article according to the larger claim 3. 13 Density is 95% of the theoretical density of aluminum nitride
A polycrystalline aluminum nitride article according to the larger claim 3. 14. The polycrystalline aluminum nitride product according to claim 4, wherein the atmosphere is nitrogen. 15 Density is 90% of the theoretical density of aluminum nitride
A polycrystalline aluminum nitride article according to the larger claim 4. 16 Density is 95% of the theoretical density of aluminum nitride
A polycrystalline aluminum nitride article according to the larger claim 4.